The present invention relates to an electrolytic gas generator (for generating, for example--hydrogen gas) which is frequency used as a source of a carrier gas in gas chromatography, a source of fuel gas for an analyzer using a flame ion detector (FID) or a flame photometric detector (FPD) and the like, a source of gas for use in physical and chemical laboratories and the like; that is to say, a supply source of a relative small and constant quantity of gas. More particularly, the present invention relates to an improve cell voltage controller in an electrolytic gas generator comprising:
an electrolytic cell for passing a predetermined electrolyte therethrough and provided with an electrode for electrolyzing the electrolyte so as to generate a desired gas therein and a gas passage communicatingly connected therewith for taking out the generated desired gas and
an electrical power supply for supplying the electrode in the electrolytic cell with electrical power for use in the electrolysis.
The basic construction of an electrolytic gas generator of this type is shown in U.S. Pat. Nos. 3,489,670 and 3,448,035, for example.
In addition, a basic voltage-controller construction, such as providing an electrical power-controller, which carries out a feedback control for a supply current on the basis of a signal corresponding to the supply current itself so that the electrical power (in this case, the current has an important meaning since electrolysis is used) for use in the electrolysis and supplied to the electrode of the electrolytic cell may be held at a predetermined design value, or providing an electrical power-controller, which carries out a feedback control for the supply current on the basis of a signal corresponding to a pressure detected by a gas pressure sensor provided in the gas passage for taking out the generated gas so that the pressure of the gas generated by the electrolytic cell may be held at a predetermined design value, is shown in U.S. Pat. No. 3,485,742, for example.
However, with an electrolytic gas generator of this kind, since it is used in specialized fields as a supply source of a relatively small and constant quantity of gas, it must be capable of stably controlling its output of gas. Accordingly, an important problem is how the control of the electrical power is precisely and stably carried out whether the feedback control for the electrical current supplied to the electrode in the above described electrolytic cell is carried out on the basis of a signal corresponding to the supply current itself or is carried out on the basis of a signal corresponding to the detected pressure of the generated gas. Accordingly, various kinds of devices have been tried in order to solve such a problem.
A recent technique, which is noteworthy in this respect, has been proposed in U.S. Pat. No. 3,870,616.
That is, a conventional electrolytic (hydrogen) gas generator according to U.S. Pat. No. 3,870,616 has a construction as shown in FIGS. 6 and 7.
Referring now to the block diagram illustrated in FIG. 6, reference numeral 01 designates an electrolytic cell for passing a predetermined electrolyte 04 (in this example, water: H.sub.2 O) supplied from an electrolytic tank 03 through an electromagnetic on-off valve 02 and provided with an electrode 05 (cathode) for electrolyzing water to evolve the desired gas, which is hydrogen gas, and an electrode (anode) 06 for evolving oxygen gas to be discharged therein so that an electrolytic membrane 07 may be held between the electrode 05 and the electrode 06. In addition, reference numeral 08 designates a hydrogen gas passage connected to the electrolytic cell 01 for taking out hydrogen gas evolved in the electrolytic cell 01 and comprising a hydrogen gas-separating trap 010 directly communicating with a liquid chamber 09 of the cathode 05 side in the electrolytic cell 01, a humidity-removing cylinder 011, a pressure switch 012 which turns ON when the gas pressure in the passage reaches at least a predetermined value, a pressure regulator 013, and a pressure gauge 014 arranged in this order. Reference numeral 015 designates a water level sensor for generating a signal when the water within the hydrogen gas-separating trap 010 reaches at least a predetermined water level so as to close the electromagnetic on-off valve 02, thereby stopping the supply of water from the electrolyte tank 03. In addition, reference number 016 designates an oxygen gas-discharging passage communicatingly connected to a liquid chamber 017 of the anode 06 side of the electrolytic cell 01 for taking out oxygen gas evolved in the electrolytic cell 01 and provided with an oxygen gas-separating trap 018 in the middle thereof. Water separated from the oxygen gas in the oxygen gas-separating trap 018 is returned to the electrolyte tank 03. Reference numeral 019 designates an electrical power supply for supplying the electrodes 05 and 06 in the electrolytic cell 01 with a current for use in the electrolysis and having an electrical power controller function for carrying out a feedback control for the supply current on the basis of the supply current itself so that the supply current to the electrodes 05 and 06 may be held at a predetermined design value and having an emergency controller function for lowering or stopping the supplying of electrical power to the electrodes 05 and 06 when the gas pressure within the hydrogen gas passage 08 reaches at least a predetermined value so as to turn ON the pressure switch 012, as described below in detail with reference to the block diagram of FIG. 7.
The electrical power supply 019 as shown in FIG. 7 comprises a power source transformer 020 for generating a transformed AC 022, which becomes the basis of the electrical power supplied to the electrodes 05 and 06 in the electrolytic cell 01 from an AC power source voltage 021 input thereto, and a DC control voltage 023 to be supplied to each of desired circuits for use in the control which will be discussed later.
In addition, reference numeral 024 designates an output network for generating the supply current for the electrodes 05 and 06 in the electrolytic cell 01 provided with an AC solid state switching device (hereinafter referred to as an SCR) 026 for converting the transformed AC voltage 022 supplied from the power source transformer 020 into a pulsating current 025 an a gate circuit 028 adapted to operate so as to output only a part (a partially switched-on divided pulsating current 027) of the pulsating current 025 generated by the SCR 026.
In addition, reference numeral 029 designates an error-detecting network provided with a basic signal-generating circuit 031 for generating a basic signal 030 corresponding to the predetermined design value from the DC voltage 023 supplied from the power source transformer 020 and a comparator circuit 036 for generating an error signal 035 corresponding to a difference between the basic signal 030 and a feedback signal 033 corresponding to an average current 032 output from the output network 024 and flowing the electrolytic cell 01. Reference numeral 037 designates a voltage controlled variable repetition frequency pulse generator for supplying a trigger pulse 038 to the gate circuit 028 in the output network 024 and adapted to output a trigger pulse 038 having a frequency corresponding to a magnitude of the error signal 035 supplied from the error detecting network 029.
In addition, the basic signal-generating circuit 031 in the error-detecting network 029 receives a detected signal from the pressure switch 012 provided in the hydrogen gas passage 08 as shown in FIG. 6 and adopts a safety-controlling construction such that the basic signal generated by the basic signal-generating circuit 031 is significantly lower than the original design value in the case where the gas pressure within the passage 08 reaches at least the predetermined value and the ON-signal from the pressure switch 012 is supplied to the basic signal-generating circuit 031, thereby lowering the supply current to the electrodes 05 and 06 in the electrolytic cell 01.
In addition, as described above, U.S. Pat. No. 3,870,616 also discloses that the feedback control for the supply current to the electrodes 05 and 06 can be carried out so as to hold the pressure of the gas generated by the electrolytic cell 01 at the predetermined design value not be feeding back the signal corresponding to the current supplied to the electrodes 05 and 06 in the electrolytic cell 01 to the comparison circuit 036 in the error-detecting network 029 and carrying out the feedback control for the supplying voltage on the basis of the supply current itself but by providing a pressure sensor 039 for detecting the gas pressure within the hydrogen gas passage 08 and feeding back a signal corresponding to the gas pressure detected by the pressure sensor 039 to the comparison circuit 036, as shown by a dotted line in FIG. 7.
In short, an electrolytic gas generator of this conventional construction is adapted to use the pulsating current 025 obtained by transforming the basically AC source voltage 021 and alternatively switching-over the transformed AC source voltage (as a result, the divided pulsating current 027 obtained by partially switching-on the pulsating current 025 by the gate) as the supplying voltage for the electrodes 05 and 06 in the electrolytic cell 01 and adopts a cell current-controller arranged such that the average current 032 supplied to the electrodes 05 and 06 is controlled so as to hold the average current 032 supplied to the electrodes 05 and 06 at a value corresponding to the design basic signal 030 by adjusting a gate-on quantity for the basic pulsating current 025 by the feedback control on the basis of the current signal corresponding to the average current 032 of the divided pulsating current 027, thereby making a relatively fine and highly responsive current control possible.
However, the electrolytic gas generator of the conventional construction has the following disadvantages:
(a) Since the pulsating current 025 having a frequency which is the same as that of the AC source voltage 021 is used as the voltage which becomes the basis of the current supplied to the electrodes 05 and 06 in the electrolytic cell 01, a large-sized and heavy transformer 020 (in this example, a power source transformer) is required:
(b) Since a peak current of the pulsating current 025 is higher (at least twice) in comparison with the average current 032 which is a substantial current supplied to the electrodes 05 and 06, various electrical constituent elements must have higher anti-current characteristics, whereby the electrical power supply 019 is apt to be large-sized and expensive as a whole coupled with the disadvantage (a);
(c) Since the construction, in which the divided pulsating current 027 is supplied to the electrodes 05 and 06 in the electrolytic cell 01, is adopted, the voltage-supplying state is apt to be fundamentally unstable;
(d) Since a control mode, in which the originally nonlinear pulsating current 025 is gated-on by a trigger pulse to obtain the divided pulsating current 027, is adopted, a linear feedback control is not carried out, thereby being apt to cause a hunting phenomenon; and
(e) Since the construction, in which the divided pulsating current 027 having a peak current higher than the average current 032 is supplied to the electrodes 05 and 06 in the electrolytic cell 01, is adopted, the heat loss power of the electrolytic cell 01 becomes comparatively large, thereby increasing the loss of electrical power and significantly reducing the useful lifetime of the electrolytic cell 01 on account of a bad influence due to the consumption of the electrolytic membrane 07 and the like.
In addition, if said pulsating current 025 is approximately calculated provided that an internal resistance of the electrolytic cell 01 is R.sub.s, the peak current of the pulsating current 027 being about 2i (i is the average current 032), and the pulsating current 025 being a square pulse repeated at a period of about 2T, the loss of electrical power (corresponding to the heat loss power) in the electrolytic cell 01 is expressed by the following equation: EQU (2i).sup.2.R.sub.s.T/2T.apprxeq.2i.sup.2 R.sub.s